Excess silicon at the Si3N4/SiO2 interface

Using electron energy loss spectroscopy, X-ray photoelectronic spectroscopy, and ellipsometry measurements, a large number of Si-Si bonds at the Si₃N₄/thermal SiO₂ interface is confirmed. After etching away the surface SiO₂ of reoxidized Si₃N₄, we found at the Si₃N₄/SiO₂ interface that the plasmon energy on the surface is 20 eV which is smaller than the bulk plasmon of either Si₃N₄ (24.0 eV) or SiO₂ (23.0 eV). From ellipsometric measurement, a large value of the refractive index (n=2.1) in the Si₃N₄/ wet SiO₂ interface layer was obtained. The effective width of the Si-rich interfacial layer is estimated to be in the range of 6-8 Å. We propose that the excess silicon at the Si₃N₄/SiO₂ interface is created by replacing nitrogen atoms with the oxygen atoms during the oxidation of Si₃N₄. Based on these observations and on numerical simulation, a hypothesis is proposed to explain the abnormally large electron capturing at the Si₃N₄/SiO₂ interface observed previously and the accumulation of positive charge at the top interface of the nitrided oxide under ionizing irradiation. © 1998 American Institute of Physics.